A grid-connected system and a method for switching operating modes of a converter thereof

Abstract

The application discloses a grid-connected system and a converter operation mode switching method thereof. The method first judges whether the grid-connected system meets preset converter operation mode switching conditions. If yes, the operation mode of each converter is switched based on the size relationship between the grid connection voltage of each converter in the grid-connected system and a preset voltage. Since the preset converter operation mode switching conditions are that the rotational inertia of the grid-connected system is less than a preset rotational inertia, the application can comprehensively consider the two factors of the rotational inertia and the grid connection voltage when the operation mode is switched, so as to reduce the influence of the large number of access of the converter on the safe and stable operation of the power grid as much as possible on the basis of ensuring the stable operation of the converter.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of switching control, in particular to a grid-connected system and a converter operating mode switching method thereof. BACKGROUND

[0002] With the continuous development of new energy technology, a large number of new energy represented by wind power and photovoltaic power are connected to the grid through grid-connected converters, resulting in the continuous increase of the penetration rate of power electronic devices in the grid. Traditional power electronic devices have weak damping and low inertia characteristics, and a large number of access to the grid brings challenges to the safe and stable operation of the grid.

[0003] Although the operating mode of the converter can be switched to a grid-forming control mode to simulate the damping and inertia characteristics of synchronous generators by using virtual synchronous machines, so that the converter has similar frequency and voltage output characteristics as synchronous generators, thereby reducing the impact on the grid, but if the virtual synchronous machine is connected to a strong grid, the damping characteristics will be weakened. Switching the operating mode of the converter to a grid-following control mode can have good dynamic and static stability in a strong grid, but the output current control characteristics will deteriorate in a weak grid, and harmonic resonance or protection shutdown and other stability problems are likely to occur.

[0004] Therefore, how to switch the grid-forming control mode and the grid-following control mode of the converter to integrate the advantages of both, and on the basis of ensuring the stable operation of the converter, to minimize the impact on the safe and stable operation of the grid after a large number of access to the grid, is a problem to be solved. SUMMARY

[0005] Based on the above-mentioned deficiencies of the prior art, the present application provides a grid-connected system and a converter operating mode switching method thereof, which can comprehensively consider the factors of rotational inertia and grid connection voltage when switching the operating mode, so as to minimize the impact on the safe and stable operation of the grid after a large number of access to the grid on the basis of ensuring the stable operation of the converter.

[0006] In order to achieve the above-mentioned purpose, the present application provides the following technical solutions:

[0007] The first aspect of the present application provides a converter operating mode switching method of a grid-connected system, comprising:

[0008] determining whether the grid-connected system meets a preset converter operating mode switching condition; the preset converter operating mode switching condition is that the rotational inertia of the grid-connected system is less than a preset rotational inertia;

[0009] If it is judged that the grid-connected system meets the preset converter operation mode switching condition, then the operation mode of each converter in the grid-connected system is switched based on the magnitude relationship between the grid connection voltage of each converter and a preset voltage.

[0010] Optionally, in the grid-connected system converter operation mode switching method described above, judging whether the grid-connected system meets the preset converter operation mode switching condition comprises:

[0011] Obtaining the moment of inertia of the grid-connected system;

[0012] Judging whether the moment of inertia of the grid-connected system is less than the preset moment of inertia;

[0013] If it is judged that the moment of inertia of the grid-connected system is less than the preset moment of inertia, then it is determined that the grid-connected system meets the preset converter operation mode switching condition;

[0014] If it is judged that the moment of inertia of the grid-connected system is not less than the preset moment of inertia, then it is determined that the grid-connected system does not meet the preset converter operation mode switching condition.

[0015] Optionally, in the grid-connected system converter operation mode switching method described above, obtaining the moment of inertia of the grid-connected system comprises:

[0016] Monitoring the moment of inertia of the grid-connected system by using a smart grid dispatching control system basic platform to obtain the moment of inertia of the grid-connected system.

[0017] Optionally, in the grid-connected system converter operation mode switching method described above, if it is judged that the grid-connected system does not meet the preset converter operation mode switching condition, then the step of judging whether the grid-connected system meets the preset converter operation mode switching condition is re-executed.

[0018] Optionally, in the grid-connected system converter operation mode switching method described above, switching the operation mode of each converter in the grid-connected system based on the magnitude relationship between the grid connection voltage of each converter and a preset voltage comprises:

[0019] Determining the grid connection voltage of each converter in the grid-connected system;

[0020] Switching the operation mode of each converter based on the magnitude relationship between the grid connection voltage of each converter and the preset voltage.

[0021] Optionally, in the grid-connected system converter operation mode switching method described above, determining the grid connection voltage of each converter in the grid-connected system comprises:

[0022] Determine the grid connection point of each converter in the grid-connected system;

[0023] The voltage of each converter's grid connection point is monitored using the smart grid dispatch and control system platform to obtain the grid connection voltage of each converter in the grid-connected system.

[0024] Optionally, in the above-described method for switching the operating mode of a grid-connected system's converter, the operating mode of each converter is switched based on the relationship between the grid connection voltage and a preset voltage, including:

[0025] If the grid connection voltage of the converter is not less than the preset voltage, the operating mode of the converter is switched to grid-connected control mode.

[0026] If the grid connection voltage of the converter is less than the preset voltage, the operating mode of the converter will be switched to the grid-type control mode.

[0027] Optionally, in the above-described method for switching the operating mode of a converter in a grid-connected system, after switching the operating mode of each converter based on the relationship between the grid connection voltage and a preset voltage of each converter in the grid-connected system, the method further includes:

[0028] The disturbance situation of the grid-connected system is monitored, and the disturbance monitoring results are obtained;

[0029] Based on the disturbance monitoring results, the control parameters of the converter in the grid-type control mode are adjusted.

[0030] Optionally, in the above-described method for switching the operating mode of a grid-connected system converter, if the grid-type control mode is virtual synchronous machine control, then based on the disturbance monitoring results, the control parameters of the converter in the grid-type control mode are adjusted, including:

[0031] If the disturbance monitoring results indicate that no disturbance has occurred in the grid-connected system, then the inertial parameters and damping parameters of the converter in the grid-type control mode will be adjusted to their initial values.

[0032] If the disturbance monitoring results indicate that a disturbance has occurred in the grid-connected system, then the inertial parameters and damping parameters of the corresponding converters are adjusted based on the virtual power angular velocity and virtual power angular acceleration of each converter under the grid-type control mode.

[0033] Optionally, in the grid-connected system converter operation mode switching method, the inertia parameter and the damping parameter of the corresponding converter are adjusted based on the virtual power angle speed and the virtual power angle acceleration of each converter in the grid-forming control mode, and the adjusting includes:

[0034] If the virtual power angle speed and the virtual power angle acceleration are both positive or negative, the inertia parameter of the corresponding converter is adjusted to a first inertia parameter value, and the damping parameter is adjusted to a first damping parameter value.

[0035] If the virtual power angle speed and the virtual power angle acceleration are not both positive or negative, the inertia parameter of the corresponding converter is adjusted to a second inertia parameter value, and the damping parameter is adjusted to a second damping parameter value.

[0036] The first inertia parameter value is greater than the second inertia parameter value, and the first damping parameter value is greater than the second damping parameter value.

[0037] Optionally, in the grid-connected system converter operation mode switching method, after adjusting the control parameters of the converter in the grid-forming control mode based on the disturbance monitoring result, the method further includes:

[0038] Returning to the step of judging whether the grid-connected system meets the preset converter operation mode switching condition.

[0039] The second aspect of the present application provides a grid-connected system, comprising: a controller and N converters, N being a positive integer; wherein:

[0040] Each of the converters is connected to a power grid, and the controller is configured to switch the operation mode of each of the converters by using the grid-connected system converter operation mode switching method disclosed in any one of the first aspect.

[0041] Optionally, in the grid-connected system, further comprising: a smart grid dispatching control system basic platform, configured to monitor the grid-connected system and each of the converters in the grid-connected system, and to provide the controller with parameters required for switching the operation mode of each of the converters by using the grid-connected system converter operation mode switching method disclosed in any one of the first aspect.

[0042] This application provides a method for switching the operating mode of a converter in a grid-connected system. The method first determines whether the grid-connected system meets the preset conditions for switching the operating mode of the converter. If so, the operating mode of each converter is switched based on the relationship between the grid connection voltage of each converter in the grid-connected system and the preset voltage. Since the preset condition for switching the operating mode of the converter is that the rotational inertia of the grid-connected system is less than the preset rotational inertia, this application can comprehensively consider both rotational inertia and grid connection voltage when switching the operating mode, so as to minimize the impact on the safe and stable operation of the grid after a large number of converters are connected to the grid while ensuring the stable operation of the converters. Attached Figure Description

[0043] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of this application. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0044] Figure 1 A flowchart illustrating a converter operation mode switching method for a grid-connected system provided in this application embodiment;

[0045] Figure 2 A flowchart for determining whether a grid-connected system meets preset converter operation mode switching conditions, provided as an embodiment of this application;

[0046] Figure 3 A detailed flowchart illustrating the switching of a converter operating mode, provided for an embodiment of this application;

[0047] Figure 4 A flowchart illustrating the determination of the grid connection voltage of a converter, provided for an embodiment of this application;

[0048] Figures 5 to 8 A flowchart of four converter operation mode switching methods for grid-connected systems provided in another embodiment of this application. Detailed Implementation

[0049] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0050] The application provides a converter operation mode switching method of a grid-connected system, which can comprehensively consider two factors of rotational inertia and grid connection voltage when switching the operation mode, so as to minimize the influence on the safe and stable operation of the grid after the grid-connected system is massively connected to the grid on the basis of ensuring the stable operation of the converter.

[0051] Please refer to Figure 1 The converter operation mode switching method of the grid-connected system mainly can include the following steps:

[0052] S101, judging whether the grid-connected system meets a preset converter operation mode switching condition.

[0053] The preset converter operation mode switching condition is that the rotational inertia of the grid-connected system is less than a preset rotational inertia.

[0054] In actual application, the specific process of executing step S101, judging whether the grid-connected system meets the preset converter operation mode switching condition, can be as shown in Figure 2 mainly includes steps S201 to S204:

[0055] S201, obtaining the rotational inertia of the grid-connected system.

[0056] In actual application, the rotational inertia of the grid-connected system can be monitored by using an intelligent grid dispatching control system basic platform to obtain the rotational inertia of the grid-connected system.

[0057] Of course, it is not limited to this, and the rotational inertia of the grid-connected system can also be obtained through other existing modes, and the application does not limit the obtaining mode, which is within the protection scope of the application.

[0058] S202, judging whether the rotational inertia of the grid-connected system is less than the preset rotational inertia.

[0059] The preset rotational inertia can be determined based on offline experience, and of course, it can also be determined according to the application environment and user demand, and the application does not limit the specific value, which is within the protection scope of the application.

[0060] It should be noted that the purpose of judging whether the rotational inertia is less than the preset rotational inertia is to determine whether the rotational inertia is lower than the set system inertia boundary value.

[0061] If it is judged that the rotational inertia of the grid-connected system is less than the preset rotational inertia, step S203 can be executed; if it is judged that the rotational inertia of the grid-connected system is not less than the preset rotational inertia, step S204 can be executed.

[0062] S203, judging that the grid-connected system meets the preset converter operation mode switching condition.

[0063] In actual application, if it is judged that the moment of inertia of the grid-connected system is less than the preset moment of inertia, it can be directly judged that the grid-connected system satisfies the preset converter operating mode switching condition.

[0064] S204, judging that the grid-connected system does not satisfy the preset converter operating mode switching condition.

[0065] In actual application, if it is judged that the moment of inertia of the grid-connected system is not less than the preset moment of inertia, it can be directly judged that the grid-connected system does not satisfy the preset converter operating mode switching condition.

[0066] It should be noted that after step S101 of judging whether the grid-connected system satisfies the preset converter operating mode switching condition is executed, if it is judged that the grid-connected system satisfies the preset converter operating mode switching condition, step S102 can be executed.

[0067] S102, switching the operating mode of each converter in the grid-connected system based on the size relationship between the grid connection voltage of each converter and the preset voltage.

[0068] In actual application, the specific process of executing step S102 of switching the operating mode of each converter in the grid-connected system based on the size relationship between the grid connection voltage of each converter and the preset voltage can be as shown in Figure 3 , mainly including steps S301 and S302:

[0069] S301, determining the grid connection voltage of each converter in the grid-connected system.

[0070] In actual application, the specific process of executing step S301 of determining the grid connection voltage of each converter in the grid-connected system can be as shown in Figure 4 , mainly including steps S401 and S402:

[0071] S401, determining the grid connection point of each converter in the grid-connected system.

[0072] Among them, for each converter, the node at the grid connection thereof can be determined as the grid connection point of the converter. Of course, it is not limited to this, but can also be customized by the user, and the specific way of determining the grid connection point of each converter in the grid-connected system is not limited in the present application, and is within the protection scope of the present application.

[0073] S402, monitoring the voltage of the grid connection point of each converter by using the smart grid dispatching control system basic platform respectively, to obtain the grid connection voltage of each converter in the grid-connected system.

[0074] In practical applications, the basic platform of the smart grid dispatch and control system can be used to monitor the voltage of the grid electrical contacts of each converter, and the monitoring results can be used as the grid connection voltage of the corresponding converter.

[0075] It should be noted that, in addition to the above-mentioned method of directly obtaining the grid connection voltage of each converter in the grid-connected system through the basic platform of the smart grid dispatch and control system, the grid connection voltage of each converter in the grid-connected system can also be determined by other existing methods. This application does not specifically limit the determination method, and all of them are within the protection scope of this application.

[0076] S302. Based on the relationship between the grid connection voltage and the preset voltage of each converter, switch the operating mode of each converter.

[0077] The specific value of the preset voltage can be determined based on offline experience, or it can be determined according to the application environment and user needs. This application does not limit its specific value, and all of them are within the protection scope of this application.

[0078] Specifically, if the grid connection voltage of the converter is not less than the preset voltage, the converter's operating mode will be switched to grid-connected control mode. If the grid connection voltage of the converter is less than the preset voltage, the converter's operating mode will be switched to grid-connected control mode.

[0079] It should be noted that when the grid connection voltage of the converter is not less than the preset voltage, it indicates that the current grid environment is likely a strong grid, and the converter's operating mode can be switched to grid-following control mode to fully utilize its advantages. Conversely, when the grid connection voltage of the converter is less than the preset voltage, it indicates that the current grid environment is likely a weak grid, and the converter's operating mode can be switched to grid-connecting control mode to fully utilize its advantages.

[0080] Based on the above principles, the converter operation mode switching method for grid-connected systems provided in this embodiment first determines whether the grid-connected system meets the preset converter operation mode switching conditions. If so, for each converter, the operation mode is switched based on the relationship between the grid connection voltage and the preset voltage. Since the preset converter operation mode switching condition is that the rotational inertia of the grid-connected system is less than the preset rotational inertia, this application can comprehensively consider both rotational inertia and grid connection voltage when switching operation modes, so as to minimize the impact on the safe and stable operation of the grid after a large number of converters are connected to the grid while ensuring the stable operation of the converters.

[0081] In addition, the existing operation mode switching scheme usually makes a judgment based on local characteristics, such as the equivalent grid impedance / short circuit ratio at the converter access point, without taking into account the overall grid information, and cannot realize overall coordination of the operation modes of all converters in the grid-connected system. The present application can take into account both the overall grid information and the local information, and can effectively realize overall coordination of the operation modes of all converters in the grid-connected system, further reducing the impact on the safe and stable operation of the grid after a large number of converters are connected to the grid, on the basis of ensuring stable operation of the converters.

[0082] It can be understood that fusing the respective advantages of network control and network following control, and determining the operation mode switching of the converter according to the actual operation of the grid, is an effective measure that takes into account the operation stability and safety, and using the equivalent grid impedance / short circuit ratio at the converter access point as the switching criterion is a basic research approach. However, the inventors have found that most of the existing researches focus on the measurement of the equivalent grid impedance / short circuit ratio at the converter access point, and do not consider directly exploiting the information of the smart grid dispatching control system basic platform (D5000 platform) to realize the operation mode switching of the converter. The present application can directly exploit the information of the smart grid dispatching control system basic platform, and use the grid connection voltage monitored in the smart grid dispatching control system basic platform as the operation mode switching parameter to realize the operation mode switching of the converter, without the need for additional measurement. This not only enables intuitive acquisition of the switching parameter, but also reduces the switching control cost to a certain extent.

[0083] Alternatively, in another embodiment provided by the present application, after step S101 of judging whether the grid-connected system meets the preset converter operation mode switching condition is performed, please refer to Figure 5 if it is judged that the grid-connected system does not meet the preset converter operation mode switching condition, the converter operation mode switching method of the grid-connected system can further include: returning to perform the step of judging whether the grid-connected system meets the preset converter operation mode switching condition, that is, returning to perform step S101.

[0084] It should be noted that after it is judged that the grid-connected system does not meet the preset converter operation mode switching condition, the step of judging whether the grid-connected system meets the preset converter operation mode switching condition can be directly or after a preset time is returned to be re-executed, so as to realize the cyclic judgment of whether the grid-connected system meets the preset converter operation mode switching condition, so as to timely perform the subsequent converter operation mode switching process after it is judged that the grid-connected system meets the preset converter operation mode switching condition.

[0085] Alternatively, in another embodiment provided by the present application, after step S102 of switching the operation mode of each converter in the grid-connected system based on the size relationship between the grid connection voltage of each converter and the preset voltage is performed, please refer to Figure 6The grid-connected system converter operation mode switching method can further include the following steps:

[0086] S501, monitor the disturbance of the grid-connected system to obtain a disturbance monitoring result.

[0087] In actual application, whether the grid-connected system is disturbed can also be monitored by the smart grid dispatching control system basic platform, so as to obtain the disturbance monitoring result.

[0088] S502, based on the disturbance monitoring result, adjust the control parameters of the converter in the grid-forming control mode.

[0089] In actual application, when the grid-forming control mode is virtual synchronous machine control, if the disturbance monitoring result indicates that the grid-connected system is not disturbed, the inertia parameter and the damping parameter of the converter in the grid-forming control mode are adjusted to the initial value.

[0090] If the disturbance monitoring result indicates that the grid-connected system is disturbed, the inertia parameter and the damping parameter of the corresponding converter are adjusted based on the virtual power angle speed and the virtual power angle acceleration of each converter in the grid-forming control mode.

[0091] It should be noted that the virtual power angle speed and the virtual power angle acceleration of each converter in the grid-forming control mode can also be calculated / monitored by the smart grid dispatching control system basic platform. The converter in the grid-forming control mode can be a virtual synchronous machine.

[0092] Specifically, based on the virtual power angle speed and the virtual power angle acceleration of each converter in the grid-forming control mode, the process of adjusting the inertia parameter and the damping parameter of the corresponding converter mainly includes case 1 and case 2:

[0093] Case 1: If the virtual power angle speed and the virtual power angle acceleration are both positive or negative, the inertia parameter of the corresponding converter is adjusted to a first inertia parameter value, and the damping parameter is adjusted to a first damping parameter value.

[0094] Case 2: If the virtual power angle speed and the virtual power angle acceleration are not both positive or negative, the inertia parameter of the corresponding converter is adjusted to a second inertia parameter value, and the damping parameter is adjusted to a second damping parameter value.

[0095] Wherein, the first inertia parameter value is greater than the second inertia parameter value, and the first damping parameter value is greater than the second damping parameter value.

[0096] It should be noted that the specific values of the first inertia parameter value and the second inertia parameter value, the first damping parameter value and the second damping parameter value can be determined according to the application environment and user requirements, and the present application does not make specific limitations, which are all within the protection scope of the present application.

[0097] Based on the above, it can be understood that, assuming that the virtual power angle speed is ω VSG , the virtual power angle acceleration is The inertia parameter is J, and the damping parameter is D. When ω VSG > 0 and Or, ω VSG < 0 and J and D are both taken as large values; when ω VSG > 0 and Or, ω VSG < 0 and J and D are both taken as small values.

[0098] It should be further pointed out that in actual application, in addition to the virtual synchronous machine control, other existing types of control can also be used for the grid-forming control mode, and the grid-forming control mode is not specifically limited in the present application, and is within the protection scope of the present application.

[0099] In the converter operating mode switching method of the grid-connected system provided in the embodiment, after the converter is switched in operating mode based on the size relationship between the grid connection voltage and the preset voltage, the adaptive adjustment of the virtual synchronous machine (grid-forming converter) moment of inertia and damping coefficient is determined based on the disturbance occurrence situation calculated / monitored by the D5000 platform and the respective sizes of the virtual power angle speed and the virtual power angle acceleration of the virtual synchronous machine, so as to improve the transient stability performance of the system.

[0100] Optionally, in another embodiment provided in the present application, after the control parameter of the converter in the grid-forming control mode is adjusted based on the disturbance monitoring result, please refer to Figure 7 The converter operating mode switching method of the grid-connected system can also return to execute the step of judging whether the grid-connected system meets the preset converter operating mode switching condition, that is, return to execute the step S101.

[0101] In actual application, after the control parameter of the converter in the grid-forming control mode is adjusted based on the disturbance monitoring result, the step of judging whether the grid-connected system meets the preset converter operating mode switching condition can be directly returned or returned after a preset time period, so as to judge whether the grid-connected system after parameter adjustment is out of the preset converter operating mode switching condition, and the operating mode switching process is re-executed when the grid-connected system is not out of the preset converter operating mode switching condition, further improving the switching control precision.

[0102] Based on the converter operating mode switching method of the grid-connected system provided in the above embodiment, assuming that the period of the grid connection voltage of each converter in the grid-connected system is 5 min, the converter operating in the grid-forming control mode is a virtual synchronous machine, and combined withFigure 8 The present invention specifically includes the following implementation process:

[0103] Step 1: Based on the smart grid dispatch and control system platform (D5000 platform), periodically obtain the rotational inertia M of the entire system.

[0104] Step 2: Set the boundary value ε1 for the entire system's rotational inertia. If M < ε1, then initiate the converter operation mode switching process, based on the voltage status V at each converter connection point i monitored by the D5000 platform. i The system switches the operating mode of some converters to network-based mode and the operating mode of others to grid-connected mode.

[0105] The process of initiating the converter operation mode switching includes the following sub-steps.

[0106] Step 2-1: Monitor the real-time voltage V at each converter connection point i based on the D5000 platform. i .

[0107] Step 2-2: If V is satisfied i If ε2 < ε2, the converter at the connection point is switched to grid-connected control mode; otherwise, it is switched to grid-following control mode. ε2 is determined based on offline experience.

[0108] Step 3: Based on the relevant algebraic or state parameters monitored / calculated by the D5000 platform, adaptively adjust the control parameters of the converter operating in the network control mode to improve the transient stability performance of the system.

[0109] Specifically, the D5000 platform is used to monitor whether the system experiences disturbances. When no disturbances occur, the converter's inertial parameter J and damping parameter D, operating in network control mode, are kept at their initial values. When a disturbance occurs, the virtual synchronous machine's virtual power angular velocity ω, calculated based on the D5000 platform, is used. VSG and virtual work angle acceleration The respective sizes of ω and D determine the settings of J and D: when ω VSG >0 and or ω VSG <0 and When ω is large, both J and D take larger values; when ω is large, both J and D take larger values. VSG >0 and or ω VSG <0 and When both J and D take smaller values.

[0110] In practice, after executing steps 2 and 3, the process can return to executing step 1, thereby achieving a loop of the entire converter operation mode switching method and further improving the switching control accuracy.

[0111] It should be noted that the total system rotational inertia M in this example is equivalent to the rotational inertia of the grid-connected system in the above embodiment, the boundary value ε1 of the total system rotational inertia is equivalent to the preset rotational inertia in the above embodiment, and the real-time voltage situation V at each converter connection point i is also relevant. i ε1 is equivalent to the grid connection voltage of the converter in the above embodiment, and ε2 is equivalent to the preset voltage in the above embodiment.

[0112] It should also be noted that the above example is only a specific application example provided by the present invention, but the application examples in actual applications are not limited to the above. They can also be modified according to the application environment and user needs. As long as the implementation method is the same as the principle and idea provided by this application, they are all within the protection scope of this application.

[0113] Optionally, another embodiment of this application also provides a grid-connected system, which may include: a controller and N converters, where N is a positive integer; wherein:

[0114] Each converter is connected to the power grid, and the controller is used to switch the operating mode of each converter using the converter operating mode switching method of the grid-connected system as described in any of the above embodiments.

[0115] In practical applications, the grid-connected system may further include a smart grid dispatch and control system basic platform. This platform monitors the grid-connected system and its individual converters, providing the controller with the parameters required for the converter operation mode switching method described in any of the embodiments, and for switching the operation modes of each converter.

[0116] The specific parameters required may be the rotational inertia of the grid-connected system and the grid connection voltage of each converter; of course, they are not limited to these, and can also be determined according to the specific application environment and user needs. This application does not make specific limitations, and all of them are within the protection scope of this application.

[0117] In practical applications, the controller can be a cloud server, a site server, or an edge layer application device; the specific application environment and user needs can be determined accordingly, and all of these are within the scope of protection of this application.

[0118] It should be noted that the relevant explanations regarding the inverter operation mode switching method for grid-connected systems can be found in the corresponding embodiments described above, and will not be repeated here. Regarding the relevant explanations of grid-connected systems, please refer to the prior art, and will also not be repeated here.

[0119] In the embodiment, since the smart grid dispatching control system basic platform is the existing equipment in the grid-connected system, the information of the smart grid dispatching control system basic platform is directly mined to realize the operation mode switching of the converter, so that the switching control cost can be reduced to a certain extent.

[0120] Those skilled in the art will further appreciate that the units and algorithm steps of the examples described in connection with the embodiments disclosed herein can be implemented in electronic hardware, computer software, or any combination thereof. To clearly illustrate the interchangeability of hardware and software, various components have been described above generally in terms of their functionality, without limitation. The specific design choices made to implement the described functionality in a concrete manner will be apparent to those skilled in the art from the description herein, but such design choices will not be described in further detail in order not to unnecessarily obscure the pertinent aspects of the examples described in connection with the embodiments disclosed herein. The examples merely set forth herein are examples and should not be construed as limiting the scope of the application, for the description herein is illustrative only and is not intended to limit the scope of the application. Rather, the scope of the application should be determined with reference to the appended claims.

[0121] In this application, the terms such as first and second, etc. are used only to distinguish one entity or operation from another, and do not necessarily require or imply these entities or operations to be in any such actual relationship or order. Moreover, the terms "comprising", "including" or any other variant thereof are intended to cover non-exclusive inclusion, so that processes, methods, articles or devices that include a series of elements not only include those elements, but also include other elements not explicitly listed or inherent to such processes, methods, articles or devices. Without more limitations, the element defined by the statement "comprising a" does not exclude the presence of additional identical elements in the process, method, article or device including the element.

[0122] The above description of disclosed embodiments enables a person skilled in the art to implement or use the present application. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to the embodiments shown herein, but will conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for switching operating modes of a converter of a grid-connected system, characterized in that, The method comprises the following steps: determining whether the grid-connected system meets preset variable flow mode switching conditions; the preset variable flow mode switching conditions are that the moment of inertia of the grid-connected system is less than a preset moment of inertia; if it is determined that the grid-connected system meets the preset variable flow mode switching conditions, then based on the magnitude relationship between the grid connection voltage of each variable flow device in the grid-connected system and a preset voltage, the operation mode of each variable flow device is switched; based on the magnitude relationship between the grid connection voltage of each variable flow device in the grid-connected system and a preset voltage, the operation mode of each variable flow device is switched, which comprises determining the grid connection voltage of each variable flow device in the grid-connected system; based on the magnitude relationship between the grid connection voltage of each variable flow device and the preset voltage, the operation mode of each variable flow device is switched; determining the grid connection voltage of each variable flow device in the grid-connected system comprises determining the grid connection point of each variable flow device in the grid-connected system; using the smart grid dispatching control system basic platform to monitor the voltage of the grid connection point of each variable flow device to obtain the grid connection voltage of each variable flow device in the grid-connected system; based on the magnitude relationship between the grid connection voltage of each variable flow device and the preset voltage, the operation mode of each variable flow device is switched, which comprises: if the grid connection voltage of the variable flow device is not less than the preset voltage, the operation mode of the variable flow device is switched to the grid-following control mode; if the grid connection voltage of the variable flow device is less than the preset voltage, the operation mode of the variable flow device is switched to the grid-constructing control mode.

2. The method of claim 1, wherein, determining whether the grid-connected system meets preset variable flow mode switching conditions comprises: obtaining the moment of inertia of the grid-connected system; determining whether the moment of inertia of the grid-connected system is less than the preset moment of inertia; if it is determined that the moment of inertia of the grid-connected system is less than the preset moment of inertia, it is determined that the grid-connected system meets the preset variable flow mode switching conditions; if it is determined that the moment of inertia of the grid-connected system is not less than the preset moment of inertia, it is determined that the grid-connected system does not meet the preset variable flow mode switching conditions.

3. The method of claim 2, wherein, obtaining the moment of inertia of the grid-connected system comprises: using the smart grid dispatching control system basic platform to monitor the moment of inertia of the grid-connected system to obtain the moment of inertia of the grid-connected system.

4. The grid-connected system inverter operating mode switching method according to claim 1, characterized by, if it is determined that the grid-connected system does not meet the preset variable flow mode switching conditions, the step of determining whether the grid-connected system meets the preset variable flow mode switching conditions is returned to be executed again.

5. The method of claim 1, wherein, after the operation mode of each variable flow device is switched based on the magnitude relationship between the grid connection voltage of each variable flow device in the grid-connected system and a preset voltage, the method further comprises the following steps: monitoring the disturbance of the grid-connected system to obtain a disturbance monitoring result; based on the disturbance monitoring result, adjusting the control parameters of the variable flow device in the grid-constructing control mode.

6. The grid-connected system inverter operating mode switching method according to claim 5, characterized by, If the network-forming control mode is a virtual synchronous machine control, based on the disturbance monitoring result, the control parameters of the converter in the network-forming control mode are adjusted, including: If the disturbance monitoring result indicates that the grid-connected system has not been disturbed, the inertia parameter and the damping parameter of the converter in the network-forming control mode are adjusted to initial values; If the disturbance monitoring result indicates that the grid-connected system has been disturbed, based on the virtual power angle speed and the virtual power angle acceleration of each converter in the network-forming control mode, the inertia parameter and the damping parameter of the corresponding converter are adjusted.

7. The grid-connected system inverter operating mode switching method according to claim 6, characterized by, Based on the virtual power angle speed and the virtual power angle acceleration of each converter in the network-forming control mode, the inertia parameter and the damping parameter of the corresponding converter are adjusted, including: If the virtual power angle speed and the virtual power angle acceleration are both positive or negative, the inertia parameter of the corresponding converter is adjusted to a first inertia parameter value, and the damping parameter is adjusted to a first damping parameter value; If the virtual power angle speed and the virtual power angle acceleration are not both positive or negative, the inertia parameter of the corresponding converter is adjusted to a second inertia parameter value, and the damping parameter is adjusted to a second damping parameter value; Wherein, the first inertia parameter value is greater than the second inertia parameter value, and the first damping parameter value is greater than the second damping parameter value.

8. The grid-connected system inverter operating mode switching method according to claim 5, characterized by, After adjusting the control parameters of the converter in the network-forming control mode based on the disturbance monitoring result, it further includes: Returning to the step of judging whether the grid-connected system meets the preset converter operating mode switching condition.

9. A grid-connected system characterized by, Including: A controller and N converters, N is a positive integer; wherein: Each of the converters is connected to the power grid, and the controller is configured to switch the operating mode of each of the converters by the converter operating mode switching method of the grid-connected system according to any one of claims 1-8.

10. The grid-connected system of claim 9, wherein, Further comprising: An intelligent power grid dispatching control system basic platform for monitoring the grid-connected system and each of the converters in the grid-connected system to provide the controller with the parameters required in the process of switching the operating mode of each of the converters by the converter operating mode switching method of the grid-connected system according to any one of claims 1-8.

Images